I have this 110 Vac Asco solenoid valve that I connected to a 24 Vdc source. The valve operated fine. I measured the current consumption with both 110Vac and 24vdc power supply: 0.2 A and 0.36 A.

What would happen if I use this AC solenoid with 24 V dc for a long period of time?

 

Try using the right coil voltage with the right voltage! I am amazed, the answer is rather obvious! Its like using a sledge hammer to pound small nails! Use the right equipment for the right job. Someone later will wonder about your skill as a technician because you should have installed a 24vdc relay instead of a 110vac relay, some of us may be wondering about that right now.

 

Responding to Sonoman's query and Matthew Hyatt's reply:

It is possible to substitute a 24-Vdc coil for a 110-Vac one in an emergency, and if the period of energization is short. I've done it a few times, but only when the substitution resulted in a current draw less than rated.

However, in your case continuous operation will probably destroy the coil because the wattage draw (I^2R) is about 40% greater, i.e., (0.36 / 0.20)^2. Thus its temperature-rise is 40% higher.

To judge the long-term effect, measure the temperature-rise over ambient and compare it to the design rating of the original coil!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

Over time, even a short period of time, your solenoid will probably overheat and fail due to the higher current draw.

 

Phil, let's examine your figures a little more closely. For the DC case we have:

P = IE = 0.36 x 24 = 8.64 Watts

We also see the coil resistance is equal to:

R = E/I = 24/0.36 = 66.67 Ohms

Now for the AC case we have:

(remember only the real part of the impedance dissipates power)

P = I^2 R = (0.2)^2 66.67 = 2.67 Watts

and we see the impedance is:

Z = E/I = 110/.2 = 550 Ohms (highly inductive)

For this case we see the dissipation is 300% higher for DC, not 40%.

For this case 8 watts may be no big deal if the valve housing is sinking heat. If it is a problem there is an easy solution. Since the field is related to the current through the coil and not the voltage across the coil, we can place a 50 Ohm, 10 W resistor in series with the coil (for DC only) and will have almost identical current (and dissipation) across the coil. The resistor can be bypassed with a capacitor if faster valve action is required.

Fred Townsend

 

Fred, thanks for the heads up.

Regarding the wattage calcs, both approaches are valid, resulting in a multiplier of 3.24. You used the I^2R approach to calculate the coil wattages for each of two operating conditions. I used the current-square law.

However, you correctly pointed out my error regarding dissipation, ie, 300 vs 40%. My faux pas was in transforming the 3.2 result into an equivalent temperature-rise. I should have said the resultant temp-rise, for a 40°C rated coil, will be about 3.2 x 40°C or about 130°C.

That said, my original response had two well-intentioned (at the time) goals:

1) To inform 'Matthew' that using a 110Vac coil in a 24Vdc circuit was possible, and it has been done.

2) To caution 'Sonoman' that in an emergency, but especially for continuous service, the current should not exceed the coil's rated value. Your suggestion of the added resistor and cap is a useful and practical one.

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])